Related Stories

Chronic cannabis use can lead to regular bouts of non-stop vomiting and an obsession with hot showers, Australian researchers have found.

General practitioner, Dr Hugh Allen of Mount Barker Hospital in South Australia, and team report this rare new syndrome in the November issue of the journal Gut.

Allen said he encountered the first case, dubbed patient Y in the paper, in the late 1990s. The patient came to him after a severe bout of vomiting.

"He would vomit continuously for two or three days," Allen told ABC Science Online. "It was so bad he had to go to hospital and be put on a drip."

Two or three months later it happened again, and then the vomiting episodes became more frequent, occurring every month.

The patient was a heavy user of marijuana at the time, said Allen, having started smoking at the age of 19 with the vomit attacks starting when he was 22.

"In all honesty, he was smoking 20 to 40 cones a day," Allen said.

When the patient was in hospital he started to act strangely, said Allen. The patient would sit in a hot shower, which he said relieved his nausea and vomiting.

"It became an obsession with him. He would have 10 to 15 showers a day."

After 15 months of cyclical vomiting, Allen said the patient concluded that his cannabis use was to blame. So he stopped using it and didn't vomit severely for nine months.

But Allen said the patient started using the drug again, and two months later was vomiting.

Behind the vomit

Allen and team set out to test the theory that chronic cannabis use could be behind otherwise unexplained cases of vomiting.

They identified 19 chronic cannabis users from the state of South Australia, which has fairly liberal laws regarding the possession of small quantities of marijuana for personal use.

Five patients refused to follow through with the study because they did not believe cannabis was behind the vomiting, said Allen.

Another five patients were excluded as there were other potential explanations for their vomiting, including schizophrenia and other drug use.

But the remaining nine cases, plus one from Sydney, demonstrated a link between chronic cannabis use and vomiting.

"They all had exactly the same syndrome," said Allen.

"Out of the 10 cases, seven abstained and all got better. Three took up smoking again and got sick again," he said. "Of these three, two gave up again and got better and one continued smoking and remained ill."

Allen said the illness, called cannabinoid hyperemesis, was "reasonably rare", affecting perhaps 1% of chronic users.

"But some people are very sensitive to cannabis."

Body temperature

Allen said experiments in mice had shown that cannabis lowers body temperature and lowered body temperature can affect how the gut works, and can lead to vomiting.

In people with vomiting sickness, cannabis could be interacting with the hypothalamus, which controls the body's temperature and gut motility, he said. And this interaction could explain why such people find relief in hot showers.

"It could be that by having a shower, people are heating themselves up and restoring their normal gut motility," said Allen.